Code in base class method not executing when using “base” keyword

Question

I'm seeing a very strange problem when overriding an abstract method and trying to call the base class's method that I'm currently overriding.

//In Dll "A"
namespace Rhino.Etl.Core.Operations
{
    using System;
    using System.Collections;
    using System.Collections.Generic;

    public class Row {}

    public interface IOperation
    {
        IEnumerable<Row> Execute(IEnumerable<Row> rows);
    }

    public abstract class AbstractOperation : IOperation
    {
        public abstract IEnumerable<Row> Execute(IEnumerable<Row> rows);
    }

    public abstract class AbstractDatabaseOperation : AbstractOperation
    {
    }

    public abstract class SqlBulkInsertOperation : AbstractDatabaseOperation
    {
        public override IEnumerable<Row> Execute(IEnumerable<Row> rows)
        {
            Console.WriteLine("SqlBulkInsertOperation");
            return rows;
        }
    }
}

//In console app "B"
namespace MyStuff
{
    using System;
    using System.Collections;
    using System.Collections.Generic;

    class Program
    {
        static void Main(string[] args)
        {
            ActualEtlOperation e = new ActualEtlOperation();
            e.Execute(new Row[0]);

            Console.ReadLine();
        }
    }

    public abstract class SqlBulkInsertWithTruncateOperation : SqlBulkInsertOperation
    {
        public override IEnumerable<Row> Execute(IEnumerable<Row> rows)
        {
            Console.WriteLine("Truncate");
            base.Execute(rows);
            return rows;
        }
    }

    public class ActualEtlOperation : SqlBulkInsertWithTruncateOperation
    {

    }
}

Basically, the SqlBulkInsertOperation does not do what I need it to do, so I need to do a little work before and after I call Execute(rows) on it by overriding it. But the code in SqlBulkInsertOperation.Execute(Rows) is not executed.

When running this code in the debugger in Visual Studio the debugger the code's not executed. When I hover the mouse over "base" in the Visual Studio editor it knows the base class is of type SqlBulkInsertOperation.

What am I missing?

Answer 1

EDIT: I've found the problem... and ironically, my "psychic debugging" comment to Eric wasn't so far off, given this blog post. Here's a short but complete program which will demonstrate what's going on...

using System;
using System.Collections.Generic;

public class Row {}

public abstract class BaseDatabaseOperation
{
    public abstract IEnumerable<Row> Execute(IEnumerable<Row> rows);
}

public abstract class SqlBulkInsertOperation : BaseDatabaseOperation
{
    public override IEnumerable<Row> Execute(IEnumerable<Row> rows)
    {
        Console.WriteLine("In SqlBulkInsertOperation.Execute");
        foreach (var row in rows)
        {
            yield return row;
        }
    }
}

public class MyOverride : SqlBulkInsertOperation
{
    public override IEnumerable<Row> Execute(IEnumerable<Row> rows)
    {
        Console.WriteLine("In MyOverride.Execute");
        return base.Execute(rows);
    }
}

class Test
{
    static void Main()
    {
        BaseDatabaseOperation x = new MyOverride();
        x.Execute(new Row[0]);
    }
}

That will print "In MyOverride.Execute" but it *won't" print "In SqlBulkInsertOperation.Execute"... because that method is implemented with an iterator block.

Of course, you can demonstrate this much more simply:

using System;
using System.Collections.Generic;

class Test
{
    static IEnumerable<string> Foo()
    {
        Console.WriteLine("I won't get printed");
        yield break;
    }

    static void Main()
    {
        Foo();
    }
}

Nothing is using the return value of the method - it's being passed back to Main, but nothing ever calls GetEnumerator() on it, and then MoveNext() on the result... so the body of the method is never executed.

See my article on iterator blocks, part two of Eric's blog post, or download chapter 6 from the home page of the first edition of C# in Depth (chapter 6 covers iterator blocks, and is free) for more details on this.

Answer 2

Here's the code I ran:

using System;
using System.Collections.Generic;
public class Row {}
public abstract class BaseDatabaseOperation 
{ 
    public abstract IEnumerable<Row> Execute(IEnumerable<Row> rows); 
} 

public abstract class SqlBulkInsertOperation : BaseDatabaseOperation 
{ 
    public override IEnumerable<Row> Execute(IEnumerable<Row> rows) 
    { 
        Console.WriteLine("base");
        return null;
    } 
} 

public class MyOverride : SqlBulkInsertOperation 
{ 
    public override IEnumerable<Row> Execute(IEnumerable<Row> rows) 
    { 
        Console.WriteLine("override");
        base.Execute(rows);
        return null;
    } 
} 

static class P 
{
    static void Main()
    {
        var m = new MyOverride();
        m.Execute(null);
    }
}

It runs fine; it produces "override" and "base".

Tell you what: modify the program I've posted here so that it produces the problem you are experiencing, and we'll analyze that. It is very difficult to analyze a problem when you cannot actually see the real code that is having problems.

Answer 3

Works fine for me. Your code needs a little cleanup - are you sure you're compiling and executing this code, and not debugging an older build of your code?

class Program
{
    public class Row { }

    public abstract class BaseDatabaseOperation
    {
        public abstract IEnumerable<Row> Execute(IEnumerable<Row> rows);
    }

    public abstract class SqlBulkInsertOperation : BaseDatabaseOperation
    {
        public override IEnumerable<Row> Execute(IEnumerable<Row> rows)
        {
            Console.WriteLine("done");
            return rows;
        }
    }

    public class MyOverride : SqlBulkInsertOperation
    {
        public override IEnumerable<Row> Execute(IEnumerable<Row> rows)
        {
            return base.Execute(rows);
        }
    }

    static void Main(string[] args)
    {
        var x = new MyOverride();
        x.Execute(null);
    }
}

Answer 4

Your example does not compile, some returns are missing, but the following modified example

public class Row
{
}

public abstract class BaseDatabaseOperation
{
    public abstract IEnumerable<Row> Execute(IEnumerable<Row> rows);
}

public abstract class SqlBulkInsertOperation : BaseDatabaseOperation
{
    public override IEnumerable<Row> Execute(IEnumerable<Row> rows)
    {
        Console.WriteLine("does useful work");
        return new Row[0];
    }
}

public class MyOverride : SqlBulkInsertOperation
{
    public override IEnumerable<Row> Execute(IEnumerable<Row> rows)
{

        Console.WriteLine("do own work here");

    //This does not execute code in base class!
        base.Execute(rows);

        return new Row[0];
}
}

Called like this:

MyOverride mo = new MyOverride();
mo.Execute(new Row[0]);

generates the output

do own work here
does useful work

You must have done something else not included in your example.

Answer 5

are these all being compiled at the same time? you might be suffering from the disconnected middle base class http://blogs.msdn.com/b/ericlippert/archive/2010/03/29/putting-a-base-in-the-middle.aspx